1. Field of the Invention
The present invention relates to a binder composition that can preferably be used in particularly molding by self-hardening.
2. Prior Art
As one conventional method of molding by self-hardening, a hardener and a binder such as phenol-formaldehyde polycondensate, phenol-formaldehyde-urea polycondensate, furfuryl alcohol-phenol-formaldehyde polycondensates, furfuryl alcohol-phenol-formaldehyde-urea polycondensate or the like are blended and mixed with a refractory granulated aggregate such as silica sand or the like to mold at room temperature.
However, the rate of hardening of the binder is generally slow in such conventional method, so molding productivity cannot be maintained at particularly at low temperatures in the winter, unless the content of sulfuric acid in a hardener composition for molding is increased to accelerate hardening. However, use of such a hardener composition for molding reduces the final strength of the resultant mold. Accordingly, the countermeasure of maintaining the productivity and the final strength of molds at practically feasible levels has been conducted for example by increasing the amount of a binder.
Under these circumstances, some binders are examined. For example, JP-A 56-56753 proposes use of a resol type phenol formaldehyde resin containing a small amount of low-molecular components. If the resol type phenol formaldehyde resin containing a small amount of low-molecular components is used, the rate of polymerization of the resin composition can be accelerated the strength of the resultant mold at an early stage can thereby be improved. However, even use of the resol type phenol formaldehyde resin containing a small amount low-molecular components does not bring about an adequate rate of hardening of a mold in winter, thus failing to achieve suitable molding productivity. To solve this, use of a hardener composition for molding with an increased content of sulfuric acid leads to a certain improvement in the rate of hardening the mold in winter, but practical mold strength cannot be achieved.
JP-B 58-46375 proposes use of a resol type phenol formaldehyde resin with a content of high molecular weight compounds with 3 or more nuclei being limited to a specific range. Use of the resol type phenol formaldehyde resin with a controlled molecular weight enables production of high-strength molds with low bad smells. However, even use of the resol type phenol formaldehyde resin with a content of high molecular weight compounds with 3 or more nuclei being limited to a specific range does not bring about an adequate rate of hardening of a mold in winter, thus failing to achieve suitable molding productivity. To solve this, use of a hardener composition for molding with an increased content of sulfuric acid leads to a certain improvement in the rate of hardening of the mold in winter, but practical mold strength cannot be achieved.
Further, even in JP-B 56-46275 and JP-B 56-46375 mentioned above, an alkali catalyst used in producing the resol type phenol formaldehyde resin is neutralized with an acid after Reaction. Its precipitates are separated by filtration or by other means, so a binder with an extremely low content of a neutralized salt has generally been used.
A thermal hardening resin composition containing an organic sulfonate for acceleration of hardening is proposed in JP-A 58-136648; a sand composition for molding having a transition metal salt of p-toluene sulfonic acid incorporated therein for the purpose of reducing consumption of heat energy and preventing generation of fin is proposed in JP-A 61-273237; and a thermal hardening composition for molding having a salt of organic sulfonic acid with a weak base incorporated therein for the purpose of improving initial strength is proposed in JP-A 3-52743. However, these methods, unlike the present invention, are related to thermal hardening methods.
In addition, U.S. Pat. No. 3,300,427 proposes an aqueous solution of resol resin containing a sulfonic acid type anion activator for the purpose of a useful process for producing a resol resin. However, unlike the present invention, this prior art is related to an aqueous solution of resol resin containing a long-chain sulfonate activator.